I have a user who was using Outlook 2003 on Windows XP SP3. She has some distribution lists (DL) in her Contacts folder with a lot of entries. Most if not all of these entries are not internal employees. She has been able to send the DL (as an attachment I presume) to people outside the organization and in their Outlook 2003 clients they were able to open the DL and see everything in it.

This user was recently upgraded to Office 2007 and when she follows the same steps in sending a DL to someone using Outlook 2003, when that person using the older client opens the DL it's blank.

Any ideas on how to resolve this?